The goal of this project is to determine mechanisms underlying the functional organization of the neural circuitry controlling a set of related but variable behaviors. In higher organisms individual muscles and muscle groups can contract in different temporal relationships to produce different behaviors at different times. This suggests that a most important aspect of neural circuitry is that it displays functional variability. However, in general, the organization of neural circuity controlling multi functional muscular systems is poorly understood. This project will test the hypothesis that a network of individually identifiable interneurons can adopt different functional circuit configurations to mediate a variety of rhythmic feeding and other oral behaviors in the snail, Helisoma. A model for a pattern generator, in the buccal ganglia of Helisoma which can account for most of variability in patterned neural activity recorded from identified motoneurons will be tested. Key aspects of the model are that the pattern generator consists of three functional subunits of interneurons that generate bursts of action potentials and evoke characteristics postsynaptic potentials in particular identified motoneurons. Subunits can be either independently active or functionally linked in a variety of ways. This project will address physiological mechanisms involved in activating, suppressing, linking, or unlinking bursting activity in different subunits of the pattern generator to produce a variety of patterns of neural activity and resultant behaviors. The effects of neuromodulators and neurotransmitters on the patterns of neural activity recorded intracellularly from identified motoneurons will be tested. The effects of different patterns of neural activity of overt behavior will be determined by behavioral analysis of video taped feeding movements made during simultaneous intracellular electrophysiological recordings from the motoneuronsl causing the movements. The long-term goal is to understand how sensory stimuli are integrated by interneurons that organize the appropriate motor response in a complex multifunctional system. Failure of appropriate coordination in such systems would lead to catastrophic disruptions of critical behaviors such as feeding, locomotion, and respiration.